I'm definitely ignorant when it comes to hunting/shooting bears of any kind so don't put a lot of faith in my advice.
But, going by things I have read, I'm sure you have enough bow for the job. So, as far as arrows go, if it were me going to Alaska to hunt big bears, I would use an arrow weighing about 11 to 13 grains per pound of draw weight and a high quality two-blade head.
Oh yeah, and I would want to get close, REAL close. But, I would most definitely want someone with a BIG rifle close by to back my @$$ up in case browney decided he might know where that sting came from! (I realize I would legally have to have a guide with a back-up rifle if I were to ever be fortunate enough to travel to Alaska to hunt big bear but I don't know about Alaska residents having to do the same)